All music that gets released today is, at a minimum, produced in stereo: two distinct channels (left and right) with the instrumentation and vocals mixed and balanced in such a way that our brains perceive the music coming from the two speakers (or headphones) in a three-dimensional way. If you have the right gear and want to spend extra, there are plenty of performances recorded in 5.1, too.
But back in the early days of rock, almost everything was recorded in mono: one unified channel with no distinct left and right sounds. This, after all, was the way music had always been recorded.
Stereo technology wasn’t introduced to vinyl until 1958. It took almost another dozen years for the idea of stereo, the home audio equipment needed to play it, and the spread of stereo FM broadcasts to become widespread enough for the record labels to dump mono entirely.
Now, though, with the resurgence of vinyl, there are reissues of mono recordings. It’s fascinating to listen and hear how much different an impact mono recordings can have—and I mean that in the most positive way possible.